Survival of seaward-migrating PIT and acoustic-tagged juvenile Chinook salmon in the Snake and Columbia Rivers: an evaluation of length-specific tagging effects

Table 1 Differences in survival rates between PIT-tagged and surgically implanted yearling and subyearling Chinook salmon

	km	Hockersmith *et al*. [12]			Hockersmith *et al*. [14]			Wargo-Rub *et al*. [15]			Wargo-Rub *et al*. [16]
Detection location	downstream	RT	PIT	P value	AT	PIT	P value	AT	PIT	P value	AT	PIT	P value
Yearling
Little Goose Dam	60	0.62	0.598	0.307	1.00	0.89	0.004	0.93	0.93	0.893	0.92	0.95	0.107
Lower Monumental Dam	106	0.554	0.507	0.591	0.88	0.83	0.222	0.92	0.88	0.08	0.88	0.93	0.096
Ice Harbor Dam	157	NA	NA	NA	NA	NA	NA	0.81	0.84	0.285	0.80	0.83	0.336
McNary Dam	225	0.328	0.343	0.427	0.70	0.79	0.102	0.72	0.78	0.054	0.68	0.75	0.095
John Day Dam	348	NA	NA	NA	0.61	0.65	0.538	0.62	0.72	0.01	0.60	0.83^a	0.001
Bonneville Dam	460	NA	NA	NA	0.48	0.54	0.547	0.50	0.63	0.001	0.52	0.75 ^a	0.021
Subyearling		Wargo-Rub *et al* . [15]
		AT	PIT	P
Little Goose Dam	60	0.65	0.81	0.003
McNary Dam	225	0.23	0.56	< 0.001

Fish were either surgically implanted with a sham radio transmitter (RT) containing an embedded PIT tag or an acoustic tag and a PIT tag (AT). All fish in these four studies were tagged at Lower Granite Dam (695 km upstream from the Pacific Ocean) and released in the Snake River just downstream of the dam. Fish were detected by PIT detectors at several downstream dams (distance downstream from release shown) on their seaward migration. The datasets from Hockersmith et al. [14] and Wargo-Rub et al. [15, 16] were used to assess length-specific tag effects.
^aIn 2008 at these two locations, the PIT data collected did not conform to statistical model assumptions and these estimates are considered problematic or inaccurate [20].
AT acoustic transmitter, NA not applicable, RT radio transmitter, PIT passive integrated transponder.